[tex]\bf sin(-\theta)\iff -sin(\theta)\qquad \qquad tan(\theta)=\cfrac{sin(\theta)}{cos(\theta)}\\\\
-----------------------------\\\\
tan(\theta)=\cfrac{sin(\theta)}{cos(\theta)}\implies cos(\theta)=\cfrac{sin(\theta)}{tan(\theta)}\quad
\begin{cases}
sin(-\theta)=\cfrac{1}{5}\\\\
-sin(\theta)=\cfrac{1}{5}\\\\
sin(\theta)=-\cfrac{1}{5}\\
--------\\
tan(\theta)=\cfrac{\sqrt{6}}{12}
\end{cases}
\\\\\\
thus\qquad cos(\theta)=\cfrac{-\frac{1}{5}}{\frac{\sqrt{6}}{12}}[/tex]
simplify away
